The present invention relates to a method for controlling a gas turbine set, in particular in gas and steam power stations, a plurality of servo elements being employed. In addition, the present invention also relates to a control device operating in accordance with this method.
A gas turbine set is a gas turbine with a generator driven by it andxe2x80x94if necessaryxe2x80x94a gearbox. Starting from a simple mechanical speed governor for a turbine and an electromechanical voltage regulator for a generator, the control devices employed in power stations, for example in gas and steam turbine installations, have been continuously improved in the course of time and adapted to the technological state of development.
In a conventional control method, the quantity of working medium flowing into the turbine is controlled by means of a turbine servo element, whose regulating variable is formed in a control circuit from the deviation between the actual output of the generator and a required output. The output, and with it the rotational speed of the generator, can therefore be controlled via the fuel quantity by means, for example, of the valve setting. In a further control circuit, a further regulating variable is formed from the deviation between the actual generator voltage and a required voltage and this further regulating variable is supplied to an exciter servo element controlling the exciter current or the exciter voltage of the generator. For this purpose, a voltage regulator can, for example, be employed which adjusts the terminal voltage of the generator by means of the excitation of the generator. The conventional control method is therefore based on control circuits which are separate from one another.
The acceptance of separate control circuits with decoupled controlled systems is permissible in the case of steam turbine sets with large thermal reservoirs provided the valves are not throttled down. The control circuits influence one another via the controlled systems built up from turbine, generator and a network fed by the generator. This can lead to the control circuits operating against one another during compensation procedures, with adverse effects on the overall control behavior. In order to compensate for this effect, a correcting variable, which is derived from the generator output, is supplied as a partial regulating variable to the exciter servo element in the conventional method. Compensation is provided for network fluctuations or changes to the slip frequency and output oscillations are damped by this means. Such output oscillations occur particularly in the case of power station installations which are coupled to an interlinking network via long lines. A circuit arrangement for damping outputoscillations in networks is described in, for example German Patent No. DE 28 51 871.
When a steam turbine is employed, the simplifying assumption of dynamic decoupling of the control circuits is still adequate for describing the overall system provided the valves are not throttled down. Where a gas turbine is used, on the other hand, undesirable coupling, which can lead to a reduction in the damping of the separate control systems, appears because of the relatively small delays or reaction times of the gas turbine as compared with the steam turbine. As an example, the bandwidth of the reactions to changes in the fuel flow in gas turbines extends into the boundary region of the generator dynamics so that the simplifying assumption of dynamic decoupling is no longer permissible. Such coupling problems also occur in the case of installations with a plurality of gas turbine sets, in particular in the case of gas and steam turbine installations. A certain influence of the control circuit of the turbine on the control circuit of the generator is achieved with the circuit arrangement described in DE 28 51 871 for damping output oscillations, is realized in a power system stabilizer damping. However, the two control circuits operate separately from one another.
Since each physical servo element, for example the valve or the exciter adjuster, has a limited regulation range, the individual servo elements can reach their limits due, for example, to regulator reactions initiated by faults or switching procedures in the network; this is always associated with a deterioration in the control behavior. The problem imposed by the limitation to the regulation range of the servo elements is even more serious in the case of multi-variable regulators because the limitations in one servo element also affect other regulating variables via the coupling in the controlled system and the regulator.
A method and a control device for controlling a turbine generator arrangement is described in European Patent No. EP 0 642 707 combining the individual regulators for rotational speed, output and voltage in a multi-variable control system is described. In the method and the control device in accordance with EP 0 642 707, changes in the controlled systems are taken into account by an adaptation strategy for the control parameters.
Particularly disadvantageous effects occur because changes in the controlled system during the operation of a power station are not always recognized unambiguously; they can therefore introduce stability problems. For this reason, the regulations of the Deutsche Verbundgesellschaft, for example, specify no switch-over of the control parameters during continuous operation.
Because of the continuing development of gas turbine technology, furthermore, there is a requirement in some cases for additional regulators, for example limiting value regulators, which supersede other regulators as soon as a regulating variable reaches its limit or as soon as physical limits to the operation of the gas turbine are exceeded. These regulators involve increased complexity, which also introduces complex changes in the regulator structure, which can in turn result in a deterioration in control quality.
An object to the present invention is to provide a method for controlling a gas turbine set, in particular in gas and steam power stations, by means of which method account is taken of the coupling in the regulation sections and, in addition, regulating variable limits and which permits reliable control of the gas turbine set. An additional object is to provide an associated control device.
A method for controlling a gas turbine set, in particular in gas and steam power stations, is provided for the technical achievement of this object. According to this method a regulating variable composed of a plurality of partial regulating variables is supplied to at least two servo elements of the gas turbine set, the partial regulating variables for each individual regulating variable being formed from control deviations by means of individual transfer functions.
In an example configuration of the present invention, the regulating variables of all the servo elements of the gas turbine set can be composed of the same number of partial regulating variables. The number of partial regulating variables corresponds to the number of control deviations, each individual regulating variable being formed from the control deviations by means of individual transfer functions. Coupling in the controlled systems and, simultaneously, reliable control of the gas turbine set is therefore provided. By this means, multi-variable control which takes account of the couplings in the controlled system by corresponding transfer functions is provided in accordance with the present invention, which multi-variable control records all the section characteristics essential to the control system and, by this means, stabilizes each operating condition of the gas turbine set.
In accordance with an advantageous configuration of the present invention, therefore, at least one f the regulating variables is additionally composed of at least one of the further regulating variables. In accordance with a further advantageous development of the present invention, at least one partial regulating variable is formed from a regulating variable. By this means, the actual, under certain circumstances limited, regulating variables are also used for the control. In this arrangement, the actual regulating variable can be measured or the limit can be simulated in the regulator so that it does not require measurement. In this way, the information about a regulating variable limit is advantageously available to the partial regulating variables. By means of the method according to the present invention, therefore, it is possible to economize on the limiting value regulators previously used in the control system.
In order to improve the control in terms of the dynamics of the overall system, the difference between the required value and the actual value of the generator output, the generator voltage, the turbine temperature and the turbine rotational speed and, where the gas turbine set is coupled to an interacting network, the generator frequency are used as control deviations. For this purpose, the respective actual values, that is the generator output delivered, the generator voltage, the turbine temperature, the turbine rotational speed and/or, where the gas turbine set is coupled to an interacting network, the generator frequency are measured and the deviation of the same from the required values demanded is formed.
In accordance with a further example embodiment of the present invention, at least one servo element for adjusting the flow of a working medium flowing into the turbine, at least one servo element for generating an exciter current or an exciter voltage for the field winding of the generator and at least one servo element adjusting the guide vanes of a compressor are used for the gas turbine set.
The object of providing a control device operating in accordance with the method according to the present invention for controlling a gas turbine set, in particular in gas and steam power stations, is achieved by providing a control device to which actual and required values of the gas turbine set are supplied as input variables and which outputs regulating variables, respectively formed from a plurality of partial regulating variables, to the servo elements of the gas turbine set. The control device includes an arrangement for forming control deviations from the required and actual values, an arrangement for generating partial regulating variables from the control deviations and an arrangement for associating a plurality of partial regulating variables to form one regulating variable.
In accordance with an example embodiment of the control device according to the present invention, the arrangement for generating the partial regulating variables from the control deviations is a control algorithm which, for example, can be deposited in a read-only memory (ROM) or in some other suitable form. Individual transfer functions, which generate the partial regulating variables as a function of the control deviations, can thus be formed for each individual regulating variable. In this way, it is possible to take account in advance of all the characteristics of the controlled system to be controlled even during the design of the control device. A control device is therefore created which can deal with all the controlled systems on which the design is based even without technically programmed adaptation strategies to adjust control parameters.